Let me just warn you, the Nexus S has a Super AMOLED screen and you can burn in the images on the screen. I have burn-in of the Time and the notification bar on my screen. it is only noticeable when i have light colored wallpaper, but it is there.

Samsung even removed the "Stay Awake" option from the Galaxy S Vibrant line (possibly others as well) in their TouchWiz UI. The Nexus S will still have it, because it is a Vanilla Android.

The screen is also one of the biggest consumers of power, so if you leave your screen on all the time, when not charging, expect to see poor battery life.